Furnace



FIG. 1 is a front perspective view of a furnace showing our new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a left side elevation view thereof; and,

FIG. 6 is a right side elevation view thereof.

The broken lines illustrate portions of the furnace that form no part ofthe claimed design.

CLAIM The ornamental design for a furnace, as shown and described.